The present invention relates generally to the reduction of emissions and improving the fuel economy of gaseous fueled engines by leaning out the combustion mixture. In particular the invention relates to an improved combustion chamber in a flat top piston which is smaller in area and deeper than a combustion chamber in a conventional piston to create a greater squish area and hence the squish velocity which improves combustion. In addition, the chamber is offset from the central axis of the cylinder to cause the swirl velocity of the combustion mixture in the vicinity of an ignition device, such as a spark plug, to be high. Finally, the combustion chamber is made non-circular in shape without resorting to one or more baffles. The non-circular shape disturbs the orderly motion of the swirl of the combustion mixture, thereby creating additional eddies and higher turbulence throughout the combustion region.
The term "baffle" as used herein, has the meaning ascribed to it by Webster's Dictionary, edited by John G. Allee, Ph.D., and copyrighted by Ottenheimer Publishers, Inc. in 1978. That meaning is defined as follows: "A plate for regulating the flow of a liquid or gas." The term "baffleless" as used herein means without a baffle.
One of the methods used in gaseous fueled engines to simultaneously reduce unwanted emissions and improve fuel economy is to increase the proportion of air as compared to the fuel or, in other words, the combustion mixture is made "lean". In general, the leaner the mixture, the better the results. The degree to which the engine can be leaned out is limited, however, by two factors: (1) stability of combustion and (2) slow flame speed.
Both of these factors are improved by increasing the turbulence of the combustible mixture at the time of ignition and immediately thereafter. Turbulence throughout the combustion volume is important with turbulence near the spark plug being particularly important and beneficial. Thus it is important to maximize the turbulence in the vicinity of the spark plug.
In the typical prior art gaseous fueled engine, the piston has a flat top and a "combustion chamber", the latter being a depression in the piston top. At top dead center, the distance between the flat top of the piston and the flat surface of the cylinder head is quite small. During the compression stroke, the fuel/air mixture is forced out of the small region above the flat top of the piston and it moves sideways at a high velocity into the combustion chamber. This movement of air is called "squish".
"Swirl" is the angular motion of the fuel/air gaseous mixture in the cylinder above the piston and/or the combustion chamber in the piston. In addition, "shear" refers to a condition where the gas velocity at one point differs significantly from the velocity at a near by point. Because of the velocity gradient, shear forces exist and cause an increase in the turbulence level. In typical prior art pistons a relatively large, relatively shallow combustion chamber is centrally located in the piston. The squish area surrounding the combustion chamber is small and is entirely at the outside perimeter of the piston while the ignition device, such as the spark plug, is normally placed at the center of the cylinder. With the prior art combustion chamber the velocity from squish is low, the shear is low and the turbulence is also relatively low particularly at the spark plug where combustion starts because the spark plug is centrally located and thus the turbulence generated by "squish" and "shear" occurs in the combustion chamber on the outer periphery of the combustion chamber which is at a point the furthest from the spark plug. In addition, the swirl is also taking place about the outer periphery of the combustion chamber at the most remote point from the spark plug. Thus the stability of combustion and flame speed are impaired.
Other prior arrangement, e.g. Alun Thomas' European patent publication No. 0111966, include structures having smaller and deeper combustion chamber recesses in which a baffle spoiling device projects. According to this patent publication, however, the geometries are so configured that the lower end of the spark plug is located in a quiescent zone near the spoiling device (baffle).
The present invention overcomes difficulties of the prior art by providing a combustion chamber which is smaller in area and deeper than in the conventional piston. As a result, the piston has a much greater squish area and hence the squish velocity and the shear forces are much greater.
In addition, the combustion chamber is off-set from the central axis of the cylinder. Thus the combustion chamber is eccentrically located with respect to the piston axis such that ignition of the fuel/air mixture by the ignition device occurs within but on the outer periphery of the combustion chamber. This causes the swirl velocity at the spark plug to be high. Further, because the combustion chamber is off-set in one direction, the squish area is off-set in the opposite direction so that the squish velocity is particularly high in the region of the spark plug. Both of these effects greatly increase the shear and the turbulence at the spark plug.
Finally, the combustion chamber is non-circular in shape. This irregular shape tends to disturb the orderly motion of the swirl thereby creating additional eddies and higher turbulence throughout the combustion region. The effect of the combination of these factors is to increase the turbulence and to increase the flame speed.
Thus it is an object of the present invention to simultaneously reduce undesirable emissions and improve fuel economy of a gaseous fueled engine.
It is another object of the present invention to simultaneously reduce undesirable emissions and improve fuel economy in gaseous fueled engines by increasing the proportion of air compared to the fuel and by increasing the stability of combustion and flame speed by increasing the turbulence of the combustible mixture at the time of ignition and immediately thereafter.
It is also an object of the present invention to provide a combustion chamber in the piston head which is smaller in area and deeper than in a conventional piston thereby providing a much greater squish area and hence squish velocity and thereby increasing the shear velocity.
It is yet another object of the present invention to eccentrically locate a combustion chamber in a head of a piston with respect to the piston axis such that ignition of the fuel/air mixture by the ignition device occurs within but on the outer periphery of the combustion chamber.
It is still another object of the present invention to provide a combustion chamber eccentrically located in the head of a piston with respect to the piston axis and which combustion chamber is non-circular in shape which tends to disturb the orderly motion of the swirl thereby creating additional eddies and higher turbulence throughout the combustion region.
It is also an object of the present invention to provide a combustion chamber eccentrically located in the head of the piston which is generally in the shape of a sector with the apex of the sector being rounded and positioned under an ignition device wherein a sector as used herein has a well-known geometrical shape.
It is yet another object of the present invention to provide a non-circular combustion chamber eccentrically located in the head of a piston with respect to the piston axis and which is generally in the shape of a sector with a squish area on all sides of the combustion chamber and with the largest squish area being adjacent the apex of the sector and nearest the ignition device.